The invention is concerned with a process for injecting a fine-grain carbon carrier including ash-bearing bituminous coal, as a reducing agent, into the hearth of a blast furnace.
In this specification, the terms brown coal and lignite may be used interchangeably, in other words a reference to brown coal may be taken to include lignite, unless the context indicates otherwise, and similarly a reference to lignite may be taken to include brown coal, unless the context indicates otherwise. In this connection it may be noted that although brown coal and lignite are generally considered as the same material, there may possibly be on recent knowledge a difference between the two kinds of material, both of which are thus encompassed by the present invention.
It has been proposed that the consumption of coke in a blast furnace can be reduced by using other fuels or by directly introducing a reducing agent into the blast furnace. However, the injection of coal into a blast furnace has hitherto been used only to a very limited degree, under practical operating conditions. This may be attributed inter alia to the fact that the preparation, transportation and distribution of fine-grain coal from a supply container into the inlet openings of the blast furnace, which are generally the tuyere arches or notches thereof, involve greater difficulties than when using a fluid agent, for example oil or gas. In addition, incomplete reaction in respect of the injected solid fuels will tend to result in noticeable disturbances and even breakdowns in operation of the blast furnace, for example due to the production of soot or black which would reduce the permeability of the blast-furnace burden in regard to the reducing gas and which may possibly also be present in the waste outlet gas. The latter can result in problems in the pieces of equipment through which the outlet gas subsequently flows.
If, for the purposes of achieving the desired saving, there may be a desire to use a cheaper bituminous coal, for example imported bituminous coal, a further difficulty is often encountered. Cheap bituminous coals usually have high ash contents which may vary between 15 and 25%, and the ash may contain predominantly acid constituents, When using bituminous coals of this kind therefore, there is the danger that the acid constituents of the ash may not be sufficiently quickly distributed in the blast furnace slag, and the resulting non-homogeneous oxide mixtures have poor flow properties and interfere with operation of the blast furnace.